Vehicle Service and Repair

Maintenance
AC Compressor Replacement Service & Repair for your Car

Car AC Compressor Replacement Service & Repair What is an AC Compressor? The AC Compressor on your car is the “heart” of your Heating Ventilation and Air Conditioning System (HVAC). Your HVAC system is also commonly referred to as an Air Conditioning System, Climate Control System, or just AC System for short. Your AC system is complex and includes many components such as: the evaporator, condenser, cooling fan, AC Compressor, line and hoses, control valves, computer and vacuum controls, receiver-drier, orifice tube or expansion valve, and various sensors and switches. For purposes of a simple explanation; the AC Compressor’s job is to compress a refrigerant gas (R12 on older cars, and R-134 since 1995 and newer cars) into a liquid to be cooled by the condenser located in front of the car’s radiator. The AC Compressor then circulates the refrigerant to the evaporator located in the passenger cabin behind the dash. The refrigerant is allowed to evaporate or decompress back into a gas in the evaporator and then it is circulated back to the AC Compressor to be compressed again. This is how you are able to get cold air. There is actually a little bit of physics involved in the process of heat transfer that occurs in the evaporator. A more detailed explanation can be referenced in another article: What is the AC System and how does it work? There are several different AC Compressor designs that can be either driven by the engine, using a drive belt, gear or shaft driven (typical on newer Audi cars) or driven by electric motors. Depending upon the car design, AC Compressors can be clutch-type (Common on BMW), variable displacement type (Common on VW), rotary ( Sometimes used on Mercedes), and scroll type. The most common AC Compressor is the clutch type. They have an electrical connector which electrically engages a clutch to ‘turn on’ or allow the AC Compressor to operate. In theory, the AC clutch is not much different from the operation of a clutch in a manual transmission. When an AC Compressor clutch fails, it is common to have to replace the entire AC Compressor unit. In the old days (before the 1990’s), mechanic shops would just replace the clutch on the AC Compressor. In modern times, the parts are generally not available anymore and the designs have increased in complexity to prevent servicing without special manufacturing equipment. All AC Compressors have some sort of piston or screw type internals for pressurizing the refrigerant. The internal mechanisms and seals can wear out or fail from time and use. This will prevent the AC Compressor form doing its job by failing to achieve proper operating pressures for the AC System. A compressor may also fail if the slightest sludge or debris is sucked into it from other components in the system deteriorating internally. Untrained or incompetent mechanics and/or the use of poorly maintained or outdated equipment can also induce debris into the system and cause AC Compressor failure. What Common Symptoms Indicate that you may need to replace the AC Compressor? • Loss of AC Oil or AC System leaks around the compressor. • No Cold air at the air vents. • Intermittent cold air or air that never seems to get cold enough. • Rattling, metallic noises, or generally loud sounds that are noticeable from the engine compartment when you turn on the Air Conditioner. How important is the AC Compressor Service or Repair? As with many broken parts issues with cars, it is best to get a failed AC Compressor fixed immediately to prevent more expensive repairs. If you suspect failure, stop using you’re AC System until you can get it repaired properly. Continued use of your AC System and Air compressor can cause it to spread debris throughout your AC System and can consequently result in many thousands of dollars of various parts replacements, including the evaporator behind your dash, hoses, and the condenser. General Repair or Service Procedure: (H2) • Scan Climate Control System for Codes and Data. • Insect and Check AC System pressures. -Add refrigerant and dye to system for diagnosis purposes. • Check AC system for leaks • Check clutch engagement of Clutch type compressor. • Check function of pressure switches and clutch circuit. • Evacuate AC System. • Remove the AC Compressor, Receiver Drier, Orifice Tube or Expansion Valve. • Flush all foreign material from the AC System. • Install New AC Compressor, New Receiver Drier, and New Expansion Valve or Orifice Tube and seals. • Evacuate and Recharge AC System. Add AC Oil or PAG OIL. • Recheck system for leaks and proper operation. Additional parts and labor that may be needed: When a component in the AC System fails, such as the Air Compressor, often debris gets circulated through system. In order to prevent immediate failure of new components and for warranty reasons, it important to replace the receiver drier and expansion valve or orifice tube. The receiver drier is like the filter for the AC System. The expansion tube and orifice tube regulate conversion of refrigerant liquid into its gaseous state and are extremely sensitive to particles larger than a micron in size. It is also necessary to flush the rest of the AC System of debris. Depending on the severity of failure, it may be prudent to replace the condenser, as it traps debris that cannot always be removed with a flush. Preventative Maintenance Recommendations: The most common reason for AC Compressor and AC system failures is failed seals or inadequate lubrication. Run your AC system periodically so that the oil in the system circulates and keeps parts lubricated. Get your car inspected as soon as you notice a change in the performance of your climate control system. ...

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